U.S. Pat. No. 3,896,131 broadly describes 6,7-dihydro-5-methyl-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxylic acids as antimicrobial agents. The patent specifically discloses several compounds substituted by halogen and/or methoxy on the benzo ring. The compound 6,7-dihydro-9-fluoro-5-methyl-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxyli c acid (now known as flumequine) which is disclosed in the aforementioned patent has received the most attention for its antimicrobial activity. It has now been found that the corresponding novel 8-methoxy-9-fluoro compound and 8-ethoxy-9-fluoro compound are much more potent and have a broader spectrum of antimicrobial activity than the compounds of the prior art.